1. Field of the Invention
The present invention relates to a power amplifier, and a microwave power amplifier with a non-linear distortion compensation function in particular.;
2. Description of the Related Art
In line with development of increasingly smaller and lighter cellular telephones in recent years, an IC supply voltage has been reduced and increasingly lower power consumption is required. As an IC supply voltage decreases, transistors composing a power amplifier become saturated more easily. Thus, the amount of noise superimposed over an amplified output signal tends to increase.
However, in order to meet stringent requirements from users, optimal communications using cellular telephones must be secured even in a low power consumption environment.
In securing the communication quality, it is important to compensate non-linear distortion of a microwave power amplifier. An example of non-linear distortion compensation circuit of a power amplifier is described in the Japanese Patent Application No.HEI 6-37551.
Suppressing non-linear distortion of the microwave power amplifier requires extraction of a distortion component signal in the first place. Then, the phase of the extracted distortion component signal is inverted. The inverted signal is superimposed over the original signal to cancel out the distortion component.
However, separating only the distortion component from the output signal of the power amplifier requires a dedicated distortion extraction circuit, which will require more circuit parts. This may increase the cost of the apparatus.
This also requires prior fine adjustment of added circuit parts. Such adjustment is troublesome.